Conventionally, an electronic device such as a personal computer includes a storage device, such as a nonvolatile semiconductor memory. Examples of the nonvolatile semiconductor memory include a flash memory capable of electrically rewriting stored content.
Referring to the nonvolatile semiconductor memory such as flash memory, the number of operations for rewriting stored content to each memory cell has an upper limit. In the case of rewriting operations for which the quantity exceeds the upper limit and are carried out for a single memory cell of the nonvolatile semiconductor memory, data written to the memory cell is not guaranteed to be held. Accordingly, restrictions for the number of rewrite operations for a memory cell correspond to the period for which the semiconductor memory may be used, that is, the life of the device.
Conventional methods for prolonging the life of a semiconductor memory are described in Japanese Laid-Open Patent Publications Nos. 2005-242897, 2003-228513 and 2009-116465, for example.
In the case in which logic 0 data stored in a memory cell of a flash memory is rewritten to logic 1 data, there are restrictions in that an erasing operation is also carried out over a whole sector including the rewritten-target memory cell. For this reason, a reduction in the number of erasing operations is desired.